FIG. 4 shows an example of known direction indicating apparatuses for automobiles or motorcycles. The direction indicating apparatus incorporates electric bulbs serving as direction indicating lamp units (blinkers) “102L” and “102R”. The direction indicating apparatus further includes indicators “105L” and “105R”, which are provided in an instrument panel.
For example, if a direction indicating switch “SW” is turned on to an L terminal, a driving current flows through two electric bulbs “102LF” and “102LR” of the direction indicating lamp unit “102L” and the indicator “105L”. As a result, the direction indicating lamp unit “102L” and the indicator “105L” blink with a period of an oscillation pulse signal supplied to a gate of an N-type MOS transistor “NM101”. If a break occurs in either of the two electric bulbs “102LF” and “102LR” of the direction indicating lamp unit “102L”, the driving current decreases. A comparator “COMP101” detects the decrease of the driving current and controls an oscillator “104a” to change the period of the oscillation pulse signal to approximately half. The direction indicating lamp unit “102L” and the indicator “105L” then blink at a rate approximately twice as high as before and thus can inform the driver of the break of the electric bulb “102LF” or “102LR”.
The direction indicating electric bulbs “102LF”, “102LR”, “102RF” and “102RR” are electric bulbs of 10 W to 27 W, for example. In the case of the electric bulbs of 10 W, if the power supply voltage is 13.5V, a current of approximately 0.74 A flows. In the case of the electric bulbs of 27 W, if the power supply voltage is 13.5V, a current of approximately 2.2 A flows. The indicators “105L” and “105R” are electric bulbs of 1.2 W to 3.4 W or LED elements of 0.02 A to 0.1 A, for example. In the case of the electric bulbs of 1.2 W, if the power supply voltage is 13.5V, a current of approximately 0.09 A flows. In the case of the electric bulbs of 3.4 W, if the power supply voltage is 13.5V, a current of approximately 0.24 A flows.
Therefore, the amount of the decrease of the driving current relatively significantly differs between when a break occurs in the direction indicating lamp unit “102L” or “102R” and when a break occurs in the indicator “105L” or “105R”. Thus, a voltage “V101” supplied to a comparator “COMP101” is set so that a break occurring in the indicator “105L” or “105R” is not detected but a break occurring in the direction indicating lamp unit “102L” or “102R” is detected.
In JP1-90831A, a known direction indicating apparatus similar to the direction indicating apparatus described above is described.
To improve the design of the body or to reduce the power consumption of the electronics, LED elements are desirably used instead of electric bulbs as direction indicating lamps of the direction indicating apparatus. However, the current flowing through the LED elements used for direction indication is approximately 0.1 A to 0.3 A, for example, and the difference between this current and the current flowing through the electric bulbs or LED elements in the indicators is less significant than the difference in the case where electric bulbs are used for direction indication.
Therefore, simply replacing the electric bulbs in the direction indicating lamps with LED elements in the arrangement of the conventional direction indicating apparatus described above is not enough to ensure that only a break in the direction indicating lamps is detected, because the amount of the decrease of the driving current does not significantly differ between when a break occurs in a direction indicating lamp and when a break occurs in an indicator. That is, when a break occurs in an indicator, the break is detected, and the rate of blinking of the direction indicating lamps increases to about twofold.